Rationale: Lupus nephritis (LuN) is the most common severe manifestation of systemic lupus erythematosus. Up to 50% of SLE patients develop LuN which usually requires toxic immunosuppressive therapies. Despite such aggressive treatments, up to 50% of LuN patients progress to renal failure within 5 years of diagnosis. We propose that these therapeutic failures reflect an incomplete knowledge of LuN pathogenesis. Goals: The goals of this Career Development Award (K08) application are to validate and iteratively develop a novel algorithm (Cell Distance Mapping - CDM) that is able to identify cognate cellular interactions between lymphocytes by means of computerized analysis, performed on images acquired from multi-channel immunofluorescent confocal laser scanning microscopy (CLSM), as recently published in Science Translational Medicine. We plan to extend this algorithm to the analysis of cognate T:dendritic cell (DC) interactions and validate it by means of using several unique systems with the first comprised of a triple adoptive transfer mouse model of cell tracker-labeled, antigen-pulsed, activated DCs, wild-type T cells, and antigen-specific T cells in the context of lymph node germinal centers. The second model is comprised of mice with sex- mismatched renal allografts combined with adoptive lymphocyte transfer, wherein we are able to restrict the response of T cells based on the gender origin of the source graft antigen(s). Finally, we propose to utilize human sex-mismatched renal allografts, wherein fluorescent in-situ hybridization techniques will allow us to determine the source of antigen-presenting cells and compare their interactions with cognate and non-cognate inflammatory cells. After iterative development of the above method, we propose to apply it to examine the characteristics and make-up of the inflammatory cell infiltrate in human LuN tubulointerstitial inflammation and renal allograft rejection, specifically focusing on the role(s) of DCs, their subtypes, and relation to T cells. We also plan to relate this information to renal disease severity and disease pathogenesis in patients. The experimental methods used for the above consist of multi-channel immunofluorescent CLSM, image analysis techniques, quantitative PCR performed on mRNA from Laser Capture Microscopy samples, as well as the use of super-resolution techniques such as Ground State Depletion Microscopy. Scientific Disciplines, Encompassed by Proposed Research: Immunology, Pathology, Medical Physics. Applicable Research Areas: Autoimmunity, inflammation, transplant immunology, image analysis, molecular and cellular biology. Trainee information: The proposed 4-year project will be performed by Dr. Vladimir Liarski, M.D., a junior faculty member at the level of Instructor and a recent Institutional Career Development Award (K12) recipient.